Sonoluminescence is a well-known phenomena discovered in the 1930's in which light is generated when a liquid is cavitated. Although a variety of techniques for cavitating the liquid are known (e.g., spark discharge, laser pulse, flowing the liquid through a Venturi tube), one of the most common techniques is through the application of high intensity sound waves.
In essence, the cavitation process consists of three stages; bubble formation, growth and subsequent collapse. The bubble or bubbles cavitated during this process absorb the applied energy, for example sound energy, and then release the energy in the form of light emission during an extremely brief period of time. The intensity of the generated light depends on a variety of factors including the physical properties of the liquid (e.g., density, surface tension, vapor pressure, chemical structure, temperature, hydrostatic pressure, etc.) and the applied energy (e.g., sound wave amplitude, sound wave frequency, etc.).
Although it is generally recognized that during the collapse of a cavitating bubble extremely high temperature plasmas are developed, leading to the observed sonoluminescence effect, many aspects of the phenomena have not yet been characterized. As such, the phenomena is at the heart of a considerable amount of research as scientists attempt to not only completely characterize the phenomena (e.g., effects of pressure on the cavitating medium), but also its many applications (e.g., sonochemistry, chemical detoxification, ultrasonic cleaning, etc.). A by-product of this research have been several patents claiming various aspects of the process. One such patent, U.S. Pat. No. 4,333,796, discloses a cavitation chamber that is generally cylindrical although the inventors note that other shapes, such as spherical, can also be used. It is further disclosed that the chamber is comprised of a refractory metal such as tungsten, titanium, molybdenum, rhenium or some alloy thereof. U.S. Pat. No. 4,333,796 does not disclose any techniques for fabricating the chamber. Similarly U.S. Pat. No. 4,563,341, a continuation-in-part of U.S. Pat. No. 4,333,796, does not disclose fabrication techniques for use with the disclosed cylindrical chamber. Rather, the patent simply discloses the preferred materials for the chamber walls and chamber linings and the preferred mounting locations for an array of acoustic horns.
U.S. Pat. No. 5,659,173 discloses a sonoluminescence system that uses a transparent spherical flask. The spherical flask is not described in detail, although the specification discloses that flasks of Pyrex®, Kontes®, and glass were used with sizes ranging from 10 milliliters to 5 liters.
U.S. Pat. No. 5,858,104 discloses a shock wave chamber partially filled with a liquid. The remaining portion of the chamber is filled with gas which can be pressurized by a connected pressure source. Acoustic transducers mounted in the sidewalls of the chamber are used to position an object within the chamber. Another transducer mounted in the chamber wall delivers a compressional acoustic shock wave into the liquid. A flexible membrane separating the liquid from the gas reflects the compressional shock wave as a dilation wave focused on the location of the object about which a bubble is formed. The shape, composition and fabrication of the shock wave chamber is not disclosed.
U.S. Pat. No. 6,361,747 discloses an acoustic cavitation reactor. The reactor chamber is comprised of a flexible tube through which the liquid to be treated circulates. The acoustic transducers are radially distributed around the tube. As disclosed, the reactor tube may be comprised of a non-resonant material such as a resistant polymeric material (e.g., TFE, PTFE), with or without reinforcement (e.g., fiberglass, graphite fibers, mica).
Although not in the field of sonoluminescence, U.S. Pat. No. 4,448,743 discloses a confinement chamber for use with an ultra-high temperature steady-state plasma. Although the plasma is referred to as a “plasmasphere”, the specification is unclear as to whether the confinement chamber is spherical or cylindrical in nature. Furthermore a method of fabricating the disclosed chamber is not provided. Rather, the patent simply discloses the design requirements for such a chamber. For example, in describing the requirements for an isochoric heating system, the patent discloses that the vessel should be capable of containing a pressure that is slowly increased from 1.82 atmospheres to 22.1 atmospheres and be fitted with infrared and far-infrared windows as well as a down-draft vertical hydrogen jet.
Although a variety of sonoluminescence systems have been designed, typically these systems are intended for low pressure research and therefore are comprised of glass or similar material. Those designed for higher pressures are usually cylindrically shaped. Those researchers who have suggested the use of spherical chambers have not disclosed how to fabricate such a chamber to enable it to handle high pressure. Accordingly, what is needed is a method of fabricating a spherical cavitation chamber that can be used for high pressure sonoluminescence. The present invention provides such a method.